I have learnt how to make the moulds cheaper and easier to build.
If you do not want to take the corners off the beds then all you need is
2 planks [12 x 2 inches ] and can be any length but I normally use 2.5m
2 iron braces
2 wooden wedges
The iron braces are the genius of the design
Now if you want to get fancy then you can build the end walls as shown in the third picture which involves cutting compound angles and using hinges
But if you want to use the moulds in a more flexible way then do not any hinges and only to make simple saw cuts on short pieces of plank as shown in pictures 4 and 5.
Keep the wall shutters apart with 2 iron braces and wooden wedges
This allows you to make circles and wiggly walls